U.S. patent number 10,181,923 [Application Number 15/293,454] was granted by the patent office on 2019-01-15 for apparatus and method for generating and using a pilot signal.
This patent grant is currently assigned to Motorola Mobility LLC. The grantee listed for this patent is Motorola Mobility LLC. Invention is credited to Vijay Nangia, Vahid Pourahmadi.
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United States Patent |
10,181,923 |
Pourahmadi , et al. |
January 15, 2019 |
Apparatus and method for generating and using a pilot signal
Abstract
A method and apparatus is for generating a modulation signal
that comprises a resource block. A resource element sequence,
M.sub.n.sup.p, of M pilot symbols is determined that corresponds to
an n.sup.th of N subcarriers. A pilot frequency domain sample
sequence, r.sub.n.sup.p, corresponding to the resource element
sequence M.sub.n.sup.p comprises a quantity, R.sub.n.sup.NZ, of
non-zero magnitude pilot frequency domain samples. R.sub.n.sup.NZ
is determined based on M and an excess bandwidth, .alpha., of an
adjacent subcarrier filter. The resource element sequence
M.sub.n.sup.p, which has no inter-subcarrier interference, is
multiplexed with N-1 resource element sequences to form the
resource block. The modulation signal is generated by modulating
each subcarrier of the N subcarriers with a corresponding resource
element sequence of the N resource element sequences and filtering
each of the modulated subcarriers using a subcarrier filter. The
resource element sequence M.sub.n.sup.p is used during receiving
for efficiently determining a channel estimate.
Inventors: |
Pourahmadi; Vahid (Urbana,
IL), Nangia; Vijay (Algonquin, IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Motorola Mobility LLC |
Chicago |
IL |
US |
|
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Assignee: |
Motorola Mobility LLC (Chicago,
IL)
|
Family
ID: |
57233878 |
Appl.
No.: |
15/293,454 |
Filed: |
October 14, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170126348 A1 |
May 4, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62248336 |
Oct 30, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
27/264 (20130101); H04L 27/2613 (20130101); H04J
13/0062 (20130101); H04L 25/03006 (20130101); H04W
72/0453 (20130101); H04L 5/005 (20130101); H04L
5/0048 (20130101); H04L 5/0007 (20130101) |
Current International
Class: |
H04J
13/00 (20110101); H04L 5/00 (20060101); H04L
25/03 (20060101); H04W 72/04 (20090101); H04L
27/26 (20060101) |
Field of
Search: |
;370/329 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Clawson; Stephen J
Attorney, Agent or Firm: Kunzler, PC
Claims
What is claimed is:
1. A method for generating a modulation signal, comprising:
determining a quantity, N, of subcarriers that are to be used for
transmitting a first resource block and a quantity, M, of resource
elements corresponding to each subcarrier of the first resource
block, wherein the first resource block comprises the N subcarriers
and M multicarrier symbols and can be used to modulate a radio
frequency (RF) carrier; determining a first resource element
sequence, M.sub.n.sup.p, of M pilot symbols in the first resource
block that corresponds to an n.sup.th of the N subcarriers, wherein
a pilot frequency domain samples sequence, r.sub.n.sup.p,
corresponding to the resource element sequence M.sub.n.sup.p,
comprises a quantity, R.sub.n.sup.NZ, of non-zero magnitude pilot
frequency domain samples, wherein R.sub.n.sup.NZ is determined
based on M and an excess bandwidth, .alpha., of an adjacent
subcarrier filter; multiplexing the first resource element sequence
M.sub.n.sup.p with the N-1 resource element sequences that
correspond to the N-1 subcarriers that are not the n.sup.th
subcarrier, to form the first resource block; and generating a
first modulation signal by modulating each of the N subcarriers
with a corresponding resource element sequence of the N resource
element sequences, which generates N modulated subcarriers, and
filtering each of the N modulated subcarriers using a corresponding
one of N subcarrier filters, wherein the N subcarrier filters
include the adjacent subcarrier filter.
2. The method according to claim 1, wherein filtering each of the N
modulated subcarriers comprises circularly filtering each modulated
subcarrier using the corresponding one of the N subcarrier
filters.
3. The method according to claim 1, where in the R.sub.n.sup.NZ
non-zero magnitude pilot frequency domain samples may not be within
any excess bandwidth region of the subcarrier and are equally
spaced about the center of the bandwidth of the subcarrier.
4. The method according to claim 1, wherein values of a pilot
signal corresponding to the n.sub.th subcarrier of the first
modulation signal in the first resource block are independent of
the values of symbols in resource element sequences of any adjacent
subcarrier.
5. The method according to claim 1, further comprising: determining
R.sub.n.sup.NZ as .times..times..alpha. ##EQU00007##
6. The method according to claim 1, further comprising: forming the
pilot frequency domain sequence r.sub.n.sup.p that comprises the
R.sub.n.sup.NZ non-zero magnitude pilot frequency domain samples
mapped as contiguous frequency samples corresponding to the
frequency samples close to the center of the pilot subcarrier and a
quantity, R.sub.n.sup.NZ, of zero magnitude pilot frequency domain
samples that is determined based on a subcarrier filter roll-off
factor and M.
7. The method according to claim 1, further comprising: determining
the R.sup.NZ non-zero magnitude pilot frequency domain samples
based on a Zadoff-Chu sequence.
8. The method according to claim 7, wherein the Zadoff-Chu sequence
has a length R.sup.NZ.
9. The method according to claim 7, wherein the Zadoff-Chu sequence
has a length less than R.sup.NZ and the R.sup.NZ non-zero magnitude
pilot frequency domain samples are a cyclic extension of the
Zadoff-Chu sequence.
10. The method according to claim 7, wherein the Zadoff-Chu
sequence has a length more than R.sup.NZ and the R.sup.NZ non-zero
magnitude pilot frequency domain samples are a truncation of the
Zadoff-Chu sequence.
11. The method according to claim 1, further comprising:
determining a second resource element sequence,
M.sub.q.sup.p:.theta.S, M pilot symbols that form a q.sup.th of the
N subcarriers, wherein q.noteq.n, and wherein pilot frequency
domain samples, r.sub.n.sup.p(i), of the q.sup.th subcarrier
corresponding to the second resource element sequence
M.sub.q.sup.p:.theta.S are each determined as at least a phase
shift, .theta.(i), of the corresponding pilot frequency domain
samples, r.sub.n.sup.p(i), of the n.sup.th subcarrier, and wherein
.theta.(i)=Qi, and wherein Q is a phase constant; and multiplexing
the second resource element sequence M.sub.q.sup.p:.theta.S with
the N-1 resource element sequences that correspond to the N-1
subcarriers that are not the q.sup.th subcarrier to form the first
resource block.
12. The method according to claim 1, further comprising:
determining a second resource element sequence,
M.sub.q.sup.p:.theta.S, of M pilot symbols that form the resource
elements for a q.sup.th one of the N subcarriers of the first
resource block, wherein q.noteq.n, and wherein the pilot symbols,
d.sub.q.sup.p, 0<i<M-1, of the q.sup.th subcarrier are each
determined as a cyclical time shift of the pilot symbols,
d.sub.n.sup.p, o<i<M-1, of the n.sup.th subcarrier; and
multiplexing the second resource element sequence M.sub.q.sup.p:TS
with the N-1 resource element sequences that correspond to the N-1
subcarriers that are not the q.sup.th subcarrier, to form the first
resource block.
13. The method according to claim 1, further comprising:
determining a second resource element sequence, M.sub.q.sup.p:CS,
of M pilot symbols that correspond to a q.sup.th of N subcarriers
of a second resource block, wherein a pilot frequency domain
samples sequence, r.sub.q.sup.p:U, corresponding to the second
resource element sequence, M.sub.q.sup.p:CS, comprises
R.sub.q.sup.NZ non-zero magnitude pilot frequency domain samples,
and wherein the R.sub.q.sup.NZ non-zero magnitude pilot frequency
domain samples of the pilot frequency domain samples sequence
r.sub.q.sup.p:U of the second resource block are determined as a
cyclical shifts of the respective R.sub.n.sup.NZ non-zero magnitude
pilot frequency domain samples of the pilot frequency domain
samples sequence r.sub.n.sup.p of the first resource element
sequence M.sub.q.sup.p of the first resource block; multiplexing
the second resource element sequence M.sub.q.sup.p:CS with the N-1
resource element sequences that correspond to the N-1 subcarriers
that are not the q.sup.th subcarrier, to form the second resource
block; and generating a second modulation signal by modulating each
subcarrier with a corresponding resource element sequence of the
second resource block, which generates N modulated subcarriers of
the second resource block, and filtering each of the N modulated
subcarriers of the second resource block using a corresponding one
of N subcarrier filters.
14. The method according to claim 13, further comprising:
modulating a first RF carrier with the first modulation signal to
generate a first modulated RF signal and coupling the first
modulated RF signal to a first antenna port; and modulating a
second RF carrier with the second modulation signal to generate a
second modulated RF signal and coupling the second modulated RF
signal to a second antenna port, wherein the second antenna port is
different than the first antenna port.
15. The method according to claim 1, further comprising:
determining a second resource element sequence, M.sub.q.sup.p:U, of
M pilot symbols that correspond to q.sup.th of N subcarriers of a
second resource block, wherein a pilot frequency domain samples
sequence, r.sub.q.sup.p:U, corresponding to the second resource
element sequence M.sub.q.sup.p:U, comprises R.sub.q.sup.NZ non-zero
magnitude values, and wherein the R.sub.n.sup.NZ non-zero magnitude
pilot frequency domain samples of the pilot frequency domain
samples sequence r.sub.n.sup.p are based on a first Zadoff-Chu
sequence having a first base, and wherein the R.sub.q.sup.NZ
non-zero magnitude pilot frequency domain samples
r.sub.q.sup.p:U(i.sub.NZ) of the pilot frequency domain samples
sequence, r.sub.q.sup.p:U are based on a second Zadoff-Chu sequence
having a second base, and wherein the first base is different than
the second base; multiplexing the second resource element sequence
M.sub.q.sup.U with the N-1 resource element sequences that
correspond to the N-1 subcarriers that are not the q.sup.th
subcarrier to form the second resource block; and generating a
second modulation signal by modulating each subcarrier with a
corresponding resource element sequence of the second resource
block, which generates N modulated subcarriers, and filtering each
of the N modulated subcarriers using a corresponding one of N
subcarrier filters.
16. The method according to claim 15, further comprising:
modulating a first RF carrier with the first modulation signal to
generate a first modulated RF signal and coupling the first
modulated RF signal to a first antenna port; and modulating a
second RF carrier with the second modulation signal to generate a
second modulated RF signal and coupling the second modulated RF
signal to a second antenna port, wherein the second antenna port is
different than the first antenna port.
17. A method for receiving a carrier demodulated RF signal,
comprising: identifying a subcarrier that includes known pilot
symbols within a resource block of the carrier demodulated RF
signal, wherein the known pilot symbols are formed to be free from
inter-subcarrier interference and forming the known pilot signals
comprises; determining a quantity, N, of subcarriers that are to be
used for transmitting a first resource block and a quantity, M, of
resource elements corresponding to each subcarrier of the first
resource block, wherein the first resource block comprises the N
subcarriers and M multicarrier symbols and can be used to modulate
a radio frequency (RF) carrier; determining a first resource
element sequence, M.sub.n.sup.p, of M pilot symbols in the first
resource block that corresponds to an n.sup.th of the N
subcarriers, wherein a pilot frequency domain samples sequence,
r.sub.n.sup.p, corresponding to the resource element sequence M,
comprises a quantity, R.sub.n.sup.NZ, of non-zero magnitude pilot
frequency domain samples, wherein R.sub.n.sup.NZ is determined
based on M and an excess bandwidth, .alpha., of an adjacent
subcarrier filter; multiplexing the first resource element sequence
M.sub.n.sup.p with the N-1 resource element sequences that
correspond to the N-1 subcarriers that are not the nlh subcarrier,
to form the first resource block; generating a first modulation
signal by modulating each of the N subcarriers with a corresponding
resource element sequence of the N resource element sequences,
which generates N modulated subcarriers, and filtering each of the
N modulated subcarriers using a corresponding one of N subcarrier
filters, wherein the N subcarrier filters include the adjacent
subcarrier filter; synchronizing to a clock of the carrier
demodulated RF signal; determining a channel estimate based on
carrier demodulated RF signal and the known pilot symbols; and
iteratively removing inter-subcarrrier interference between at
least two subcarriers of data symbols without determining a new
channel estimate.
18. An apparatus, comprising: a processing system comprising a
processor and a memory, wherein the memory includes program
instructions that control the processor to determine a quantity, N,
of subcarriers that are to be used for transmitting a first
resource block and a quantity, M, of resource elements
corresponding to each subcarrier of the first resource block,
wherein the first resource block comprises the N subcarriers and M
multicarrier symbols and can be used to modulate a radio frequency
(RF) carrier, determine a first resource element sequence,
M.sub.n.sup.p, of M pilot symbols in the first resource block that
corresponds to an n.sup.th of the N subcarriers, wherein a pilot
frequency domain samples sequence, r.sub.n.sup.p, corresponding to
the resource element sequence M.sub.n.sup.p, comprises a quantity,
R.sub.n.sup.NZ, of non-zero magnitude pilot frequency domain
samples, wherein R.sub.n.sup.NZ is determined based on M and an
excess bandwidth, .alpha., of an adjacent subcarrier filter,
multiplex the first resource element sequence M.sub.n.sup.p with
the N-1 resource element sequences that correspond to the N-1
subcarriers that are not the n.sup.th subcarrier, to form the first
resource block, and generate a first modulation signal by
modulating each of the N subcarriers with a corresponding resource
element sequence of the N resource element sequences, which
generates N modulated subcarriers, and filtering each of the N
modulated subcarriers using a corresponding one of N subcarrier
filters, wherein the N subcarrier filters include the adjacent
subcarrier filter; and an RF final stage that modulates an RF
carrier with the first modulation signal to generate a modulated RF
signal, amplifies the modulated RF signal to generate an amplified
RF signal, and couples the amplified RF signal to an antenna.
19. A non-transitory computer readable media comprising programmed
instructions that when executed by a processor performs:
determining a quantity, N, of subcarriers that are to be used for
transmitting a first resource block and a quantity, M, of resource
elements corresponding to each subcarrier of the first resource
block, wherein the first resource block comprises the N subcarriers
and M multicarrier symbols and can be used to modulate a radio
frequency (RF) carrier; determining a first resource element
sequence, M.sub.n.sup.p, of M pilot symbols in the first resource
block that corresponds to an n.sup.th of the N subcarriers, wherein
a pilot frequency domain determining a first resource element
sequence, M.about., of M pilot symbols in the first resource block
that corresponds to an n.sup.th of the N subcarriers, wherein a
pilot frequency domain samples sequence, r.sub.n.sup.p,
corresponding to the resource element sequence M.sub.n.sup.p,
comprises a quantity, R.sub.n.sup.NZ, of non-zero magnitude pilot
frequency domain samples, wherein R.sub.n.sup.NZ is determined
based on M and an excess bandwidth, .alpha., of an adjacent
subcarrier filter; multiplexing the first resource element sequence
M.sub.n.sup.p with the N-1 resource element sequences that
correspond to the N-1 subcarriers that are not the n.sup.th
subcarrier, to form the first resource block; and generating a
first modulation signal by modulating each of the N subcarriers
with a corresponding resource element sequence of the N resource
element sequences, which generates N modulated subcarriers, and
filtering each of the N modulated subcarriers sing a corresponding
one of N subcarrier filters, wherein the N subcarrier filters
include the adjacent subcarrier filter.
Description
FIELD OF THE INVENTION
The present invention relates generally to data transmission and
reception, and more specifically to the use of a pilot signal to
provide channel estimation at a receiver.
BACKGROUND
Pilot signals (or reference signals) are commonly used in data
transmissions to allow a receiver to make an estimate of
characteristics of a radio channel in which the data is
transmitted, allowing improved reception accuracy. For the proposed
version of transmission scheme known as Generalized Frequency
Division Multiplexing (GFDM), two pilot schemes have been
discussed, a preamble technique and a scattered pilot symbol
technique with interference pre-cancellation. The preamble
technique is based on adding pilot symbols (time division
multiplexed symbols that occupy all subcarriers or a significant
portion of the carrier bandwidth) as a preamble to a modulated data
block. The scattered pilot symbol technique adds pilot symbols
(frequency division multiplexed) within a multiplexed data block.
Each technique has certain advantages and drawbacks. In particular,
the preamble technique allows reuse of known preamble techniques
but has the possibility of higher overhead and out of band
emissions. The scattered pilot symbol with interference
pre-cancellation may provide fairly efficient overhead but may
incur a power penalty and additional hardware for high dynamic
range between subcarriers. Furthermore, the use of this scheme for
multiple antennas is unclear.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying figures, where like reference numerals refer to
identical or functionally similar elements throughout the separate
views, together with the detailed description below, are
incorporated in and form part of the specification, and serve to
further illustrate embodiments of concepts that include the claimed
invention, and explain various principles and advantages of those
embodiments. The description is meant to be taken in conjunction
with the accompanying drawings in which:
FIG. 1 is a functional block diagram that shows a transmitter
section of an electronic device, in accordance with certain
embodiments.
FIG. 2 is a functional block diagram that shows a receiver section
of an electronic device, in accordance with certain
embodiments.
FIG. 3 is a hardware block diagram that shows a portion of an
electronic device, in accordance with certain embodiments.
FIG. 4 is a hardware block diagram that shows a portion of an
electronic device, in accordance with certain embodiments.
FIG. 5 is a time-frequency representation of one example of a small
resource block, in accordance with certain embodiments.
FIG. 6 is a frequency plot that shows subcarrier filter gain
characteristics and digital sample magnitudes at discrete sampling
points of a modulated resource block, in accordance with an
embodiment.
FIG. 7 is a frequency plot that shows subcarrier filter gain
characteristics and digital sample magnitudes at discrete sampling
points of a modulated resource block that has been generated using
a discrete Fourier transform, in accordance with some
embodiments.
FIG. 8 is a flow chart that shows some steps of a method for
generating a modulation signal, in accordance with some
embodiments.
FIGS. 9-15 are flow charts that show some additional steps that may
be performed in the method described with reference to FIG. 8, in
accordance with some embodiments.
FIG. 16 is a flow chart that shows some additional steps of the
method for generating a modulation signal described with reference
to FIG. 15, in accordance with some embodiments.
FIG. 17 is a flow chart shows some steps that may be used in the
method for generating a modulation signal described above with
reference to FIG. 8, in accordance with some embodiments.
FIG. 18 is a flow chart that shows some additional steps of the
method for generating a modulation signal described with reference
to FIG. 17, in accordance with some embodiments.
FIG. 19 is a flow chart that shows some steps of a method for
receiving a carrier demodulated RF signal, in accordance with some
embodiments.
Skilled artisans will appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of the embodiments.
DETAILED DESCRIPTION
In the description below, like reference numerals are used to
describe the same, similar or corresponding parts in the several
views of the drawings. Numerous specific details are set forth to
provide a full understanding of the subject technology. It will be
obvious, however, to one ordinarily skilled in the art that the
subject technology may be practiced without some of these specific
details. In other instances, well-known structures and techniques
have not been shown in detail so as not to obscure the subject
technology.
Embodiments described herein generally relate to generating and
using pilot symbols within Generalized Frequency Division
Multiplexing (GFDM) protocols, which may include Cyclic Prefix
Orthogonal Frequency Division Multiplexing (CP-OFDM) and Single
Carrier Frequency Division Multiplexing (SC-FDM protocols). Certain
embodiments describe using one or more subcarriers exclusively for
pilot symbols, wherein the pilot symbols are designed to avoid
inter-subcarrier interference.
Referring to FIG. 1, a functional block diagram 100 shows a
transmitter section 110 of an electronic device 105, in accordance
with certain embodiments. The electronic device 105 may a
transmitter only device, such as, for one example, a cellular base
station transmitter. Another example would be a low power sensor,
such as a medical or environmental monitor. The electronic device
105 may be an electronic device that has an associated transmitter,
such as any type of personal two way communication device,
including but not limited to cellular telephones, tables, and
computers. The electronic device 105 may be operating at any radio
carrier frequency. The transmitter section 110 comprises a resource
block modulator 120 that accepts as an input a series of data
symbols 115, each of which may be complex values (just one example
of such complex valued symbols are symbols that are 16-QAM
(quadrature amplitude modulated)). The resource block modulator 120
determines values 116 which characterize resource blocks currently
being formed from the series of data symbols 115. Using the values
116, the resource block modulator 120 generates one or more data
symbol sequences and determines one or more pilot symbol sequences
(or reference symbol sequences) from stored data or by calculation.
The pilot symbol sequences are formed in accordance with unique
techniques described more fully below that render them largely free
from inter-subcarrier interference. The data symbol sequences and
pilot symbol sequences are used by the resource block modulator 120
to form modulated resource blocks 121. A resource element sequence
is one of either a data symbol sequence or a pilot symbol
sequence.
The values 116 may include two integer values, M and N, which
define, respectively, a quantity of resource element time slots (or
symbol-block length) and a quantity of subcarriers of the resource
blocks currently being formed, as well as information (such as a
base subcarrier frequency and subcarrier separation or subcarrier
spacing) that determines characteristics of subcarrier frequencies,
as well as subcarrier filter characteristics. The values 116 that
characterize the resource blocks that are being formed and the
pilot symbol sequences may be determined from values stored
persistently within the electronic device 105, such as in a table,
or that are stored transiently by the electronic device 105, such
as data received by the electronic device 105 in a control message.
Each of the one or more pilot symbol sequences is associated with a
different one of the N subcarriers. These may be termed pilot
subcarriers. The subcarriers in general are typically arranged as
adjacent subcarriers, but pilot subcarriers are typically
non-adjacent to other pilot subcarriers. The data symbols may
represent a wide variety of types of information, such as audio
(music, voice, etc.), video (camera images, TV, etc.) and telemetry
(environmental sensors, radar results, etc.).
Each resource block is then used to generate one of the modulated
resource blocks of signal 121, as follows. Each resource element
sequence (pilot or data symbol sequence) of a resource block is
separately pulse shaped with a filter {tilde over (g)}[n] where
{tilde over (g)}[n] is a circular filter with a period M.times.N.
The time period for each symbol is a reciprocal of the subcarrier
frequency spacing. A resulting symbol block can be written as
follows:
.function..times..times..times..function..times..function..times..times..-
times..pi..times. ##EQU00001## In equation (1), k is the index that
identifies modulated resource element samples, n is the index that
identifies specific subcarriers, and i is the index for time slots
(each time slot has the time period of a symbol). More than one
pilot symbol sequence may be included in each resource block, at
intervals that have been determined to be at most the minimum
needed such that radio channel characteristics determined for the
pilot subcarriers provide sufficiently accurate representations of
the radio channel characteristics of the one or more subcarriers
comprising data symbols. A cyclical prefix is added to form a
complete modulated resource block of signal 121. The coherence time
of the radio channel (i.e., the time duration over which the radio
channel is assumed to be sufficiently constant) is assumed
typically to be at least the symbol-block length (M time periods)
such that the radio channel can be assumed to be almost constant
over the symbol-block. Subcarriers with no associated symbol
sequence are not modulated and are considered as null subcarriers.
The modulated resource block of signal 121 is coupled to an RF
modulator 125, which mixes it with carrier reference 122, which may
be a quadrature reference signal. The resulting modulated RF
carrier signal 126 is coupled to an RF power amplifier 130. The
resulting amplified modulated RF carrier signal is coupled to an
antenna 135 and radiated. An RF final stage comprises the RF
modulator 125, the RF power amplifier 130, and the antenna 135.
In some embodiments, such as Multiple Input, Multiple Output (MIMO)
embodiments, modulated resource blocks in signal 121 are generated
for simultaneous transmission using the same RF carrier frequency.
The pilot symbol sequences in each resource block intended for
simultaneous transmission are determined in a manner described
below that renders pilot symbol sequences of equivalent subcarriers
in the different resource blocks (intended for simultaneous
transmission) as orthogonal or largely orthogonal. The data symbol
sequences and possibly the pilot symbol sequences of the two or
more resource blocks in signal 121 intended for simultaneous
transmission may be precoded, for example, by applying a precoding
matrix. The two or more resource blocks in signal 121 intended for
simultaneous transmission are modulated and the modulated signals
are coupled to RF modulators 145 (not shown in FIG. 1) and
amplifiers 150 (not shown in FIG. 1) to generate simultaneous
modulated RF signals that are amplified and coupled to additional
antennas (not shown in FIG. 1) for transmission. The multiple
modulated RF signals may comprise identical data symbols or
differing data symbols, depending on system configuration (e.g.,
diversity versus spatial division multiplexing). In MIMO
embodiments or single transmitter embodiments, one antenna may be
used for both transmission and interception by including a duplexer
per receive-transmit signal pair, as is known in the art.
Referring to FIG. 2, a functional block diagram 200 shows a
receiver section 210 of an electronic device 205, in accordance
with certain embodiments. The electronic device 205 may a receiver
only device, such as, for one example, a cellular base station
receiver. Another example could be an alert device. The electronic
device 205 may be an electronic device that has an associated
transmitter, such as any type of personal two way communication
device, including but not limited to cellular telephones, tables,
and computers. The electronic device 205 may be operating at any
radio carrier frequency. The receiver section 210 comprises an
antenna 215 that intercepts RF energy and converts it to an RF
signal 216 that is coupled to an RF amplifier 220 (e.g., a low
noise RF amplifier). The RF signal 216 is amplified by the RF
amplifier 220, generating an amplified RF signal 221 that is
coupled to an RF demodulator 225. The RF demodulator uses a carrier
signal 227 (which may be a quadrature signal) to demodulate the
amplified RF signal 221, generating an RF demodulated signal 226
that includes sequential modulated resource blocks. The modulated
resource blocks are such as those described above with reference to
FIG. 1, but they have been altered by radio channel
characteristics, inter-subcarrier interference, and noise.
The RF demodulated signal 226 is coupled to a channel estimator 230
and to a symbol recovery function 235. The channel estimator 230
and symbol recovery function 235 determine values 231 which
characterize the modulated resource blocks currently being received
by the receiver section 205. The values 231 may include the same
information described above with reference to FIG. 1 and values
116. Using the values 231, the channel estimator 230 determines
from stored data or by calculation one or more known pilot symbol
sequences that are expected to be in each resource block. The
channel estimator 230 uses the known pilot symbol sequences to
determine one or more channel estimates 232 from the RF demodulated
signal 226 corresponding to the one or more known pilot sequences
in each sequential resource block. The pilot symbol sequences are
pilot symbol sequences that have been determined in accordance with
unique techniques described with reference to FIGS. 1 and FIGS.
8-18. The pilot symbol sequences that are being used may be
determined from persistent memory within the electronic device 205,
such as in a table, by using the values 231. The values 231 may be
received in a control signal or may be determined from persistent
memory within the electronic device, such as another table, using
protocol identification received in a control signal.
Alternatively, the pilot symbol sequences may be generated by the
channel estimator function 230 or the data symbol recovery function
235 based on the values 231.
The symbol recovery function 235 uses the values 231 to
characterize the resource blocks being received. The symbol
recovery function 235 recovers the sequences of data symbols 236
from each sequential resource block using the characterization of
the resource blocks (from the values 231) being received and the
channel estimates made by the channel estimator 230 for each pilot
sequence. This is done by an iterative process that removes
adjacent subcarrier interference between adjacent data symbol
modulated subcarriers, without having to re-calculate channel
estimates made from the pilot symbol modulated subcarriers, because
inter-subcarrier interference is avoided for pilot symbols, as
described below. The recovered data symbols 236 may represent a
wide variety of types of information, such as described above with
reference to data symbol types in FIG. 1. In some embodiments, such
as Multiple Input, Multiple Output (MIMO) embodiments, one or more
modulated RF signals are simultaneously received from multiple
antennas. The multiple modulated RF signals may comprise identical
data symbols or differing data symbols, depending on the protocol
(e.g., diversity reception versus spatial division reception). In
these MIMO embodiments, the channel estimator uses the values 231
and the RF demodulated signals 226 to make channel estimates 232
for each pilot sequence in each simultaneously received resource
block. The symbol recovery function 230 then recovers the data
symbols 236 for each resource block of the MIMO transmission.
Interference between pilot symbol sequences in simultaneously
transmitted and received RF signals is avoided or minimized by
techniques described below. In MIMO embodiments or single
transmitter embodiments, one antenna may be used for both
transmission and interception by included a duplexer per
receive-transmit signal pair, as is known in the art.
Referring to FIG. 3, a hardware block diagram 300 shows a portion
of an electronic device 305, in accordance with certain
embodiments. The electronic device 305 may be any of those
described above with reference to FIG. 1. The portion of the
electronic device 305 comprises a processing system 325, a
digital-to-analog (D/A) converter 330, and among other things,
receives the series of data symbols 115, receives the values 116,
and generates a modulated resource block in signal 121 as described
with reference to FIG. 1. The processing system 325 comprises a
processing function 310 and memory 315. The processing function 310
comprises one or more processing devices (only one is shown in FIG.
3), each of which may include such sub-functions as central
processing units (cores), cache memory, instruction decoders, just
to name a few. The processing function 310 executes program
instructions which may be located within memory in the processing
devices or may be located in a memory 315 external to the
processing function 310, to which the memory 315 is
bi-directionally coupled, or in a combination of both. The memory
315 may be any combination of hardware that stores programming
instructions, such as RAM, ROM, EPROM, EEPROM, and parts of an
ASIC. The processing function 310 may, in some embodiments, be
coupled to the D/A convertor 320 as a separate device, and is
typically coupled to other functions of the electronic device not
shown in FIG. 3.
The hardware block diagram 300 (FIG. 3) shows the executable
operating instructions (EOI) 316 being stored in the memory 315,
external to the processing function 310, but as noted above, the
memory 315 may be within or shared with the one or more processing
devices. The memory 315 also stores data 394. The EOI 316 of the
electronic device 305 includes groups of instructions identified as
an operating system (OS) 390, software applications 392 (including
software utilities), and a software application called the resource
block modulator 393. The applications 392 may include conventional
radio applications and may include human interface applications.
Examples of conventional radio applications include standby
applications and radio control applications. Examples of human
interface applications include display and keyboard applications,
game applications, navigation application, video processing
applications, and sensor processing applications. In some
embodiments, the human interface applications are executed in a
separate processing system. The processing function 310 includes
input/output (I/O) interface circuitry (not explicitly shown) that
is controlled by the processing function 310. The I/O circuitry is
coupled to the signal 115 conveying the series of data symbols and
may be coupled to the digital-to-analog (D/A) convertor 330 by
signal 326. In some embodiments, the D/A convertor 330 is a portion
of the processing function 310.
The processing system 325 runs the resource block modulation
application 393, which performs the functions of the resource block
modulator 120 (FIG. 1) of electronic device 105 (FIG. 1), except
D/A conversion when a separate D/A convertor 330 is used. A first
embodiment of the resource block modulator 120 comprises that
portion of the processing system 325 necessary to perform the
functions of the resource block modulator 120, and specifically
includes the operating instructions of the resource block
modulation application 393. A second embodiment of the resource
block modulator 120 comprises the D/A convertor 330 and that
portion of the processing system necessary to perform the remaining
functions of the resource block modulator 120, and specifically
includes the operating instructions of the resource block
modulation application 393.
Referring to FIG. 4, a hardware block diagram 400 shows a portion
of an electronic device 405, in accordance with certain
embodiments. The electronic device 405 may be any of those
described above with reference to FIG. 2. The portion of the
electronic device 405 comprises a processing system 425, an
analog-to-digital (A/D) converter 430, and among other things,
receives a RF demodulated signal as signal 226, receives values
231, and generates recovered data symbols 236 as described with
reference to FIG. 2. The processing system 425 comprises a
processing function 410 and memory 415. The processing function 410
comprises one or more processing devices (only one is shown in FIG.
4), each of which may include such sub-functions as central
processing units (cores), cache memory, instruction decoders, just
to name a few. The processing function 410 executes program
instructions which may be located within memory in the processing
devices or may be located in a memory 415 external to the
processing function 410, to which the memory 415 is
bi-directionally coupled, or in a combination of both. The memory
415 may be any combination of hardware that stores programming
instructions, such as RAM, ROM, EPROM, EEPROM, and parts of an
ASIC. The processing function 410 may, in some embodiments, be
coupled to the A/D convertor 420, and is typically coupled to other
functions of the electronic device not shown in FIG. 4.
The hardware block diagram 400 (FIG. 4) shows the executable
operating instructions (EOI) 416 being stored in the memory 415,
external to the processing function 410, but as noted above, the
memory 415 may be within or shared with the one or more processing
devices. The memory 415 also stores data 494. The EOI 416 of the
electronic device 405 includes groups of instructions identified as
an operating system (OS) 490, software applications 492 (including
software utilities), and a software application called the
receiving application 493. The receiving application 493 comprises
two sub-applications, a channel estimator application and a symbol
recovery application. The applications 492 may include conventional
radio applications and may include human interface applications.
Examples of conventional radio applications include standby
applications and radio control applications. Examples of human
interface applications include display and keyboard applications,
game applications, navigation application, video processing
applications, and sensor processing applications. In some
embodiments, the human interface applications are executed in a
separate processing system. The processing function 410 includes
input/output (I/O) interface circuitry (not explicitly shown) that
is controlled by the processing function 410. The I/O circuitry is
coupled to the RF demodulated signal 226 and may be coupled to the
A/D convertor 430 by signal 426. In some embodiments, the A/D
convertor 430 is a portion of the processing function 410.
The processing system 425 runs the receiving application 493, which
performs the functions of the channel estimator function 230 (FIG.
2) and symbol recovery function 235 (FIG. 2) of electronic device
205 (FIG. 2), except A/D conversion when a separate D/A convertor
430 is used. A first embodiment of the channel estimator function
230 and symbol recovery function 235 comprises that portion of the
processing system 425 necessary to perform the functions of the
channel estimator function 230 and symbol recovery function 235,
and specifically includes the operating instructions of the
receiving application 493. A second embodiment of the resource
block modulator 120 comprises the A/D convertor 430 and that
portion of the processing system necessary to perform the remaining
functions of the channel estimator function 230 and symbol recovery
function 235, and specifically includes the operating instructions
of the receiving application 493.
Referring to FIG. 5, a time-frequency representation 500 of one
example of a small resource block 505 is shown, in accordance with
certain embodiments. The small resource block 505 shown in FIG. 5
has four subcarriers 510. The number of subcarriers 510 is
identified as N in this document. In this example, N=4. The number
of time slots 515 or symbol-block length in this document is
indicated by M. In this example, M=5. Each resource element may be
a pilot symbol or a data symbol. A set of multicarrier resource
elements modulated on the N subcarriers is transmitted
simultaneously in each time slot. Resource elements that are data
symbols are designated as d.sub.n (i), whereas resource elements
that are pilot symbols are designated as d.sub.n.sup.p(i). In these
designations, 0.ltoreq.n<N and 0.ltoreq.i<M. Resource element
520, d.sub.3 (3), is specifically referenced in FIG. 5 as an
example. In these representations, p indicates a pilot symbol, n
indicates a specific subcarrier, and the i within d.sub.n (i)
indicates a specific time slot. A lack of superscript indicates a
data symbol. In the time period at the left of the representation,
a block CP is identified. This is a representation of a cyclic
prefix in the time domain of a certain duration (e.g., typically a
fraction of the time slot duration) that precedes the M time slots
or symbol-block in the time domain and is a replica of the samples
at the end of symbol-block of duration equal to the cyclic prefix
duration. In this small resource block 505 there is only one pilot
sequence on one pilot subcarrier. The inclusion of one pilot
sequence on one pilot subcarrier may be used in circumstances in
which a channel estimate made by a receiver using the pilot symbols
of the one pilot sequence on the pilot subcarrier is expected to
characterize the channel for subcarriers 0, 2, and 3 sufficiently
well to allow adequate recovery of all the data symbols in the
resource block 505. This expectation may be based on several
characteristics of the environment in which the resource block is
transmitted, for example, the RF carrier frequency, the RF
bandwidth (which is typically closely related to the sum of the
bandwidths of the subcarriers), the nature of multipath in the RF
channel, the filter characteristics of the subcarrier filters, etc.
In large resource blocks, a multiplicity of pilot symbol sequences
or pilot subcarriers may be used. In some embodiments, location or
position of the pilot subcarrier(s) on different resource blocks
may be different. In some embodiments, location or position of
pilot subcarrier(s) of a resource block of a first symbol-block may
be different than the location or position of pilot subcarrier(s)
of the resource block of a second symbol-block. The location or
position of pilot subcarrier(s) may be determined by a
predetermined hopping sequence which may be based on an Identity of
an electronic device or an Identity signaled by an electronic
device.
Referring to FIG. 6, a frequency plot 605 shows subcarrier filter
gain characteristics and digital sample magnitudes at discrete
sampling points of a modulated resource block that has been
generated using a Discrete Fourier Transform, in accordance with an
embodiment. The gain axis 610 shows subcarrier filter gains
normalized to a maximum value of 1. The frequency axis 615 shows
frequencies normalized to a frequency equal to one subcarrier
bandwidth or subcarrier spacing. This embodiment is presented to
show problems solved with other embodiments described below. In
this example, the N and M values for the resource block are the
same as described with reference to FIG. 5, i.e., N=4 and M=5. For
clarity and simplicity, in this example all data and pilot
frequency domain samples are assumed to have had a magnitude of 1
prior to modulation and filtering. The subcarrier filters have gain
characteristics 620-623 in this example and are identical for all
subcarriers, are circular filters, and are root-raised cosine
filters (with excess bandwidth factor or rolloff factor
.alpha.=0.3), which provides pulse shaping approximately as shown
in FIG. 6, and use an upconversion factor of two. The filter having
gain characteristic 620 is a filter for 5 filtered frequency domain
samples 635-639 of the 10 upconverted filtered frequency domain
samples r.sub.0 (i), 0.ltoreq.i<10 of a data resource element
sequence, d.sub.0 (i), 0.ltoreq.i<5. The filter having gain
characteristic 621 is a filter for the 10 upconverted filtered
frequency domain samples 650-659, r.sub.1.sup.p(i),
0.ltoreq.i<10, of a pilot resource element sequence,
d.sub.1.sup.p(i), 0.ltoreq.i<5. The filter having gain
characteristic 622 is a filter for 5 filtered frequency domain
samples 670-674 of the 10 upconverted filtered frequency domain
samples r.sub.2 (i), 0.ltoreq.i<10 of a data resource element
sequence, d.sub.2 (i), 0.ltoreq.i<5. Five filtered sample values
for the first and third subcarrier resource element sequences and
all filtered data samples for the fourth subcarrier resource
element sequence are not shown, for simplicity and clarity.
It will be appreciated that the sample values generated as signal
326 (FIG. 3) are combined values that are the weighted sum of the
values of the filtered symbols occurring from subcarriers at a same
sample time. The frequency domain representation of the signal 326
comprises samples that are combined values of the sum of the values
of the filtered samples occurring from adjacent subcarrier. For
some frequency-domain samples, the combined value is equal to the
value of only one of the two filtered samples because the other
filtered sample has a value of zero due to filtering. However,
there are regions of excess bandwidth, .alpha., which is a measure
of excess bandwidth of the subcarrier filter, of which two excess
bandwidth regions 690, 691 are shown in FIG. 6. The excess
bandwidth regions 690, 691 are the regions of a filter gain
characteristic beyond the Nyquist bandwidth of half symbol rate
(i.e., half subcarrier spacing) to a frequency at which the gain
reaches zero or an insignificant value. In the present case of
adjacent subcarrier filters, the subcarrier filters are arranged
such that the Nyquist bandwidth edges of two adjacent filters are
at a boundary frequency. The excess bandwidth of a filter is
quantified herein as a fraction, .alpha., of the excess bandwidth
of the filter to the Nyquist bandwidth. It will be appreciated that
the total value of a sample that falls within this excess bandwidth
region is the sum of the filtered sample values from two resource
element sequences; for example, one being a data symbol sequence on
subcarrier n=0 and the other (subcarrier n=1) being a pilot symbol
sequence. This overlap between the adjacent subcarrier filters
contributes to the amounts of inter-subcarrier interference between
the data symbol sequence and pilot symbol sequence.
If this set of transmitted sample values were received by a
receiver, the receiver would be attempting to recover a pilot
symbol sequence that has interference from data symbol sequence(s)
from adjacent subcarrier(s). This makes the process of reception
complex, because an iterative process must be used to derive a
first pass estimate of the channel characteristics using samples of
the received pilot symbol sequence and the known pilot symbol
sequence on the pilot subcarrier, which gives an incorrect estimate
of the channel characteristics because of the interference, in
addition to the noise. The incorrect estimated channel
characteristic may then be used to recover the data symbol
sequence(s) that are interfering with the pilot symbol sequence.
The recovered data symbol sequence may be incorrect due to the
incorrect channel estimate and noise. The recovered data symbol
sequence may then be used to remove the data subcarrier
interference from the pilot subcarrier using the known subcarrier
filter characteristics. This improves the quality of the received
pilot symbol sequence and in turn improves the channel estimate
which is based on the improved (interference-reduced) pilot symbol
sequence. This process may be iterated as much as needed to achieve
a desired pilot symbol sequence quality, but the resulting data
symbol error rate may still be higher than desired and the recovery
of the channel estimate is complicated and therefore resource
consuming.
In some embodiments a general expression for the signal 121 (FIG.
1) for a pilot sample sequence r.sub.n.sup.p(i) for subcarrier
n.di-elect cons.{1, . . . , N} is given in equation (2), which is
derived from a Discrete Fourier Transform of equation (1):
r.sub.n.sup.p(i)=(P.sup.(n-1).GAMMA..sub.Tx.sup.(L)R.sup.(L)W.sub.Md.sub.-
n-1+P.sup.(n).GAMMA..sub.Tx.sup.(L)R.sup.(L)W.sub.Md.sub.n+P.sup.(n+1).GAM-
MA..sub.Tx.sup.(L)R.sup.(L)W.sub.Md.sub.n+1) (2) In equation (2)
i={nM+l}, l.di-elect cons.{-M, M-1}, R.sup.(L)={I.sub.M, I.sub.M, .
. . , I.sub.M}.sup.T,
.upsilon..upsilon..times..times..upsilon..times..upsilon..times..pi..time-
s..times..gamma. ##EQU00002## .GAMMA..sup.(L)=W.sub.LMg.sup.(L),
I.sub.M is an Identity matrix of size M, L is the upconversion
factor (in our example L=2), W.sub..upsilon. is a DFT-matrix of
size .upsilon., g.sup.(L) is the down-sampled (by factor N/L)
version of the filter coefficient g, and P.sup.(n) is a permutation
matrix for up-converting the n.sup.th sub-carrier to its respective
sub-carrier frequency. The coherence time of the channel is
preferably at least the resource symbol-block length such that the
channel can be assumed to be constant over the symbol-block. From
this equation, it can be seen that the ten samples for each
subcarrier are a sum of values related to the subcarrier and
adjacent subcarriers. In FIG. 6, the values 639, 640, 670, 671,
which are samples for the adjacent channels, have insignificant
magnitudes due to filtering, so in this embodiment there are four
sample times at which non-zero values would be added together by
equation (2) to get the sample values that occur in signal 326. The
sample pairs that are added together at these four sample times are
(637, 652), (638, 653), (657, 672), and (658, 673).
Referring to FIG. 7, a frequency plot 705 shows subcarrier filter
gain characteristics and digital sample magnitudes at discrete
sampling points of a modulated resource block that has been
generated using a Discrete Fourier Transform, in accordance with
some embodiments. The gain axis 610 and frequency axis 615 are the
same as in FIG. 6. In this example, the subcarrier filters are
identical to those described with reference to FIG. 6. The N and M
values for the resource block are the same as described with
reference to FIG. 5, i.e., N=4 and M=5. For clarity and simplicity,
in this example all non-zero magnitude data and pilot frequency
domain samples are shown as if they had magnitude of 1. This is not
the actual situation, as will be made clear below. A significant
difference between these embodiments and the embodiment described
with reference to FIG. 6 is that the only pilot frequency domain
samples having non-zero values before filtering are determined such
that they are in the region 792 of the pilot subcarrier filter gain
characteristic 621 that is between the defined minimum thresholds
of the excess bandwidths 690, 691 of the adjacent subcarrier
filters. In the example being used, the pilot sample sequence
r.sub.n.sup.p, (n=1) has non-zero magnitude samples only for pilot
samples r.sub.n.sup.p(1), 4.ltoreq.i.ltoreq.6, identified in FIG. 7
as pilot samples 754. 755, 756. All other pilot samples,
r.sub.n.sup.p(1), 0.ltoreq.i.ltoreq.3 and r.sub.n.sup.p(1),
7.ltoreq.i.ltoreq.9, which are identified in FIG. 7 as 750, 751,
752, 753 and 757, 758, 759, have zero magnitude prior to filtering.
The filtered sample values of the data samples in the adjacent
subcarriers have the same values as shown in FIG. 6. As a result of
the constraint that the only pilot frequency domain samples having
non-zero values before filtering are not within the excess
bandwidth regions, it will be appreciated that the pilot time
domain symbol sequence incurs no interference from adjacent
subcarrier data or pilot symbol sequence in the same resource
block. This constraint may be achieved in some embodiments as
described in the following techniques.
Referring to FIG. 8, a flow chart 800 of some steps of a method for
generating a modulation signal is shown, in accordance with some
embodiments. The modulation signal is one such as signal 121 (FIG.
1), generated by an electronic device such as electronic device 105
(FIG. 1). At step 805, a quantity, N, of subcarriers that are to be
used for transmitting a first resource block and a quantity, M, of
resource elements corresponding to each subcarrier of the first
resource block are determined. The first resource block comprises
the N subcarriers and M multicarrier symbols, and can be used to
modulate a radio frequency (RF) carrier. In this context, "first"
simply serves to distinguish one resource block from another, not
to identify a relative time of occurrence of the resource block. A
multicarrier symbol comprises N symbols of the same time slot (one
or more of which may be pilot symbols). A first resource element
sequence, M.sub.n.sup.p, of M pilot symbols is determined at step
810 in the first resource block that corresponds to an n.sup.th of
the N subcarriers. A pilot frequency domain sample sequence,
r.sub.n.sup.p, corresponding to the resource element sequence
M.sub.n.sup.p comprises a quantity, R.sub.n.sup.NZ, of non-zero
magnitude pilot frequency domain samples. R.sub.n.sup.NZ is
determined based on M and an excess bandwidth, .alpha., of an
adjacent subcarrier filter. The adjacent subcarrier filter is one
that is used to filter a modulated subcarrier that is adjacent to
the n.sup.th subcarrier within the first resource block. The first
resource element sequence M.sub.n.sup.p is multiplexed at step 815
with the N-1 resource element sequences that correspond to the N-1
subcarriers that are not the n.sup.th subcarrier, to form the first
resource block. At step 820 a first modulation signal is generated
by modulating each subcarrier of the N subcarriers with a
corresponding resource element sequence of the N resource element
sequences. This generates N modulated subcarriers. Each of the N
modulated subcarriers is filtered using a corresponding one of N
subcarrier filters, wherein the N subcarrier filters include the
adjacent subcarrier filter. In some embodiments, a second resource
block is modulated with a different multi-carrier transmission
scheme (e.g., OFDM of SC-FDM). In some embodiments, one or more
guard (or null) subcarriers may be introduced between adjacent
resource blocks. This may help to reduce the interference between
adjacent resource blocks. In some embodiments, the guard (or null)
subcarriers may be created by setting the value of the resource
element sequence of an edge subcarrier of one or more resource
blocks to zero or null. In some embodiments, a first device is
allocated a first set of contiguous resource blocks and a second
device is allocated a second set of contiguous resource blocks
adjacent to the first set of contiguous resource blocks, and one or
more guard (or null) subcarriers are introduced at the boundary
between the first set of contiguous resource blocks and second set
of contiguous resource blocks. The guard (or null) subcarriers may
be edge subcarrier corresponding to the boundary resource block(s)
of the first device and second device resource allocation.
The R.sub.n.sup.NZ non-zero magnitude pilot frequency domain
samples may not be within any excess bandwidth region of the
subcarrier and are equally spaced about the center of the bandwidth
of the subcarrier. The R.sub.n.sup.NZ non-zero magnitude pilot
frequency domain samples are contiguous in frequency. The values of
the time domain pilot signal corresponding to the n.sup.th
subcarrier of the first modulation are independent of the values of
data symbols in adjacent subcarriers.
The time domain pilot symbols are symbols for which the
R.sub.n.sup.NZ non-zero magnitude pilot frequency domain samples
meet the stated constraints (the number of non-zero pilot frequency
domain samples is determined based on combinations of M and
.alpha.). The time domain pilot symbols may be obtained by first
forming the complete pilot frequency domain sample sequence
r.sub.n.sup.p by zero padding the R.sub.n.sup.NZ non-zero magnitude
pilot frequency domain samples by a quantity R.sub.n.sup.Z of zero
magnitude pilot frequency domain samples. In an example in which
the subcarrier filter span is characterized over two subcarrier
spans corresponding to an upconversion factor of two,
R.sub.n.sup.Z=2M-R.sub.n.sup.NZ. The zero padded pilot sample
sequence may then be transformed by an inverse Discrete Fourier
Transform, which may be performed in some embodiments as an Inverse
Fast Frequency Transform, to generate the pilot symbol sequence,
M.sub.n.sup.p. In some embodiments this process to determine the
time domain pilot symbols may be carried out during a design phase
for all expected combinations of M, N, and .alpha. at the time of
design of a protocol and the results stored as a look up table. The
determination of the pilot symbols may then be accomplished in an
electronic device 105 by determining a set of M and .alpha. values
for a particular transmission, and using the look up table to
determine the pilot symbols. The pilot symbols may then be used to
perform the multiplex operation to assemble all the symbols for a
resource block. This technique provides a common procedure to
prepare the modulation signal 121. This is an efficient process for
generating resource blocks that have pilot sequences that have
reduced or no inter-subcarrier interference. In contrast, it will
be appreciated that the modulated values of signal 121 within any
subcarrier that is not a pilot subcarrier is dependent on resource
element sequence values (such as symbol values) in adjacent
subcarriers (if any) that are not pilot subcarriers, due to the
subcarrier filters. Alternatively, the electronic device may
determine the pilot symbol sequence by making a determination of
the values of M and .alpha., and determining the value
R.sub.n.sup.NZ therefrom using any method, such as a graphical
method or any one of several techniques described herein, to
establish values for each of the R.sub.n.sup.NZ samples, such as
heuristically or by any one of several techniques described herein
below, and performing an Inverse Discrete Fourier Transform to
generate the pilot symbols.
In some embodiments, the subcarrier filters have identical gain and
bandwidth characteristics. In some embodiments, the filters are
root-raised cosine filter (for example with excess bandwidth
factor, or roll-off factor .alpha.=0.3). In some embodiments, the
filter characteristics, including excess bandwidth, and the values
of M and N are determined by the selection of a particular
protocol, which may be influenced by information from a network
controlling device and/or information determined by the electronic
device. For example, the type of data to be communicated influences
the values M and N. The bandwidth resources that are available for
a particular session or message may influence the number of
subcarriers, N, and may influence the subcarrier bandwidth and
subcarrier filter characteristics. The value of M may be based on
the amount of data that is in a particular message or data packet.
The complete time domain signal (signal 121, FIG. 1) is the
summation of all pilot (and data) signals on the different
subcarriers. The summation is typically performed in the discrete
time domain, so that signal 326, FIG. 3, may also be considered to
the summation of the time domain signals.
Referring to FIG. 9, a flow chart 900 shows a step of the method
that may be used in the method for generating a modulation signal
that is described above with reference to FIG. 8, in accordance
with some embodiments. At step 905, filtering each of the N
modulated subcarriers (step 820, FIG. 8) comprises circularly
filtering each modulated subcarrier using the corresponding one of
the N subcarrier filters.
Referring to FIG. 10, a flow chart 1000 shows a step of the method
that may be used in the method for generating a modulation signal
that is described above with reference to FIG. 8, in accordance
with some embodiments. In embodiments in which all subcarrier
filters are identical and the subcarrier filters are characterized
over two subcarrier spans, R.sub.n.sup.NZ may be determined (step
810, FIG. 8) as
.times..times..alpha. ##EQU00003## For embodiments in which the
subcarrier filters do not have equivalent excess bandwidths for the
two adjacent subcarrier filters, the formula would be based on the
values for .alpha. for the subcarrier filters (i.e., subcarrier
filter for subcarrier of interest, and adjacent subcarrier
filters). In one example in which M=5 and .alpha.=0.3,
R.sub.n.sup.NZ=3.
Referring to FIG. 11, a flow chart 1100 shows a step of the method
that may be used in the method for generating a modulation that is
described above with reference to FIG. 8, in accordance with some
embodiments. At step 1105, the pilot frequency domain sequence
r.sub.n.sup.p is formed that comprises the R.sub.n.sup.NZ non-zero
magnitude pilot frequency domain samples mapped as contiguous
frequency samples corresponding to the frequency samples close to
the center of the pilot subcarrier and a quantity, R.sub.n.sup.Z,
of zero magnitude pilot frequency domain samples that is determined
based on a subcarrier filter rolloff factor and M. A method of
determining R.sub.n.sup.Z is described above with reference to FIG.
8. The frequency samples encompassing the center frequency sample
of the pilot subcarrier may comprise equally spaced frequency
samples that in some embodiments with an odd number of frequency
samples have equal number of frequency samples on both upper and
lower frequency portions around the center frequency sample and in
other embodiments with an even number of frequency samples have
unequal number of frequency samples (difference of one sample) on
the upper and lower frequency portions around the center frequency
sample of the pilot subcarrier. The zero magnitude frequency
samples may be distributed equally or unequally (e.g., difference
of one sample) outside of the non-zero magnitude frequency
samples.
Referring to FIG. 12, a flow chart 1200 shows some steps that may
be used in step 810 of the method for generating a modulation
signal described above with reference to FIG. 8, in accordance with
some embodiments. At step 1205, the R.sub.n.sup.NZ non-zero
magnitude pilot frequency domain samples are determined based on a
Zadoff-Chu sequence of length L and base u. A Zadoff-Chu sequence,
x.sub.u(m), of length L and base u can be given as,
.function..times..times..pi..times..times..function. ##EQU00004##
m=0, 1, 2, . . . , L-1 (1.ltoreq.u.ltoreq.L-1). At optional step
1210, in some embodiments, L=R.sub.n.sup.NZ and base u is
relatively prime with respect to L. In some embodiments, the
Zadoff-Chu sequences are determined using a base that is relatively
prime with reference to R.sub.n.sup.NZ. At step 1215, the
Zadoff-Chu sequence in some embodiments has a length less than
R.sub.n.sup.NZ (e.g., the Zadoff-Chu sequence length L is given by
the largest prime number such that L<R.sub.n.sup.NZ) and the
R.sub.n.sup.NZ non-zero magnitude pilot frequency domain samples
are a cyclic extension of the Zadoff-Chu sequence, x.sub.u(n mod
L), 0.ltoreq.n<R.sub.n.sup.NZ. At step 1220, in some embodiments
the Zadoff-Chu sequence has a length more than R.sub.n.sup.NZ
(e.g., the Zadoff-Chu sequence length L is given by the smallest
prime number such that L>R.sub.n.sup.NZ) and the R.sub.n.sup.NZ
non-zero magnitude pilot frequency domain samples are a truncation
of the Zadoff-Chu sequence (x.sub.u(n),
0.ltoreq.n<R.sub.n.sup.NZ). It will be appreciated that the
Inverse Discrete Fourier Transform of a Zadoff-Chu sequence of
length L results in a sequence of time symbols of constant
amplitude, and for which cyclical shifts of the pilot time symbols
or pilot frequency domain samples are orthogonal, respectively, to
other shifts. Cyclic extension and truncation somewhat degrades
these aspects. Zadoff-Chu is alternatively designated ZC in this
document.
In some embodiments, the R.sub.n.sup.NZ non-zero magnitude pilot
frequency domain samples are determined based on a pre-determined
QPSK (Quadrature Phase Shift Keying) modulation sequence. In some
embodiments, the R.sub.n.sup.NZ non-zero magnitude pilot frequency
domain samples are scrambled by a pseudo-random scrambling
sequence. The pseudo-random scrambling sequence may be based on an
Identity of an electronic device or an Identity signaled by an
electronic device. The pseudo-random scrambling sequence may be a
complex scrambling sequence such as a QPSK scrambling sequence with
in-phase and quadrature-phase sequences based on a real valued
pseudo-random sequence, for example, determined from a PseudoNoise
(PN) sequence or Gold sequence generator.
One consequence of forming pilot symbol sequences with the type of
shaping of the pilot signal in frequency domain describe herein
(i.e., the quantity of non-zero frequency domain samples
R.sub.q.sup.NZ is less than M) for a smaller number of non-zero
frequency domain samples than M, is that it is possible that the
signals on different time slots (d.sup.p (i),
0.ltoreq.i.ltoreq.M-1) have different powers. For instance, for a
selected frequency response of a length-5 symbol-block (M=5) for
which R.sub.q.sup.NZ=3, wherein a first value for the base u of a
Zadoff-Chu sequence is used, a scaled r.sub.u.sup.p(n)=(1.291,
-0.645-1.118i, 1.291). In the time domain,
d.sup.p(n)=(0.8660-0.5000i, 0.2388+0.4446i, -0.8534+1.0085i,
0.0976-1.3175i, -0.3490+0.3645i). So, the corresponding power of
each time slot of the length-5 symbol-block would be (1, 0.504,
1.32, 1.32, 0.504). As can be seen, although the total power (in
time) is the same as the power that exists for data subcarriers, it
is not constant over different time-slots. To reduce or remove this
time dependency when multiple pilot signals are used (e.g., in a
resource block, or across resource blocks) an appropriate phase
shift may be applied to the r.sub.u.sup.p(n) such that for
different pilot subcarriers a time-shifted version of the
time-domain representation of the original pilot signal are
generated, i.e.:
d.sub.n.sup.p=.eta..times..sub.u.sup.(.beta.,n)(1:2:2M) (3)
In equation (3), .eta. is a normalization factor to compensate for
the zero-padding in the frequency domain, and
.sub.u.sup.(.beta.,n)(n)=IFFT (e.sup.-jnkr.sub.u.sup.p(n)) with a
cyclic shift of .beta.. For instance, as for the above example,
equation (3) gives the following pilot sequences:
d.sub.1.sup.p=Seq1=(0.86-0.50i,0.23+0.44i,-0.85+1.00i,0.09-1.31i,-0.34+0.-
36i)
d.sub.2.sup.p=Seq2=(-0.34+0.36i,0.86-0.50i,0.23+0.44i,-0.85+1.00i,0.0-
9-1.31i)
d.sub.3.sup.p=Seq3=(0.09-1.31i,-0.34+0.36i,0.86-0.50i,0.23+0.44i,-
-0.85+1.00i)
d.sub.4.sup.p=Seq4=(-0.85+1.00i,0.09-1.31i,-0.34+0.36i,0.86-0.50i,0.23+0.-
44i)
d.sub.5.sup.p=Seq5=(0.23+0.44i,-0.85+1.00i,0.09-1.31i,-0.34+0.36i,0.8-
6-0.50i)
d.sub.6.sup.p=Seq6=(0.86-0.50i,0.23+0.44i,-0.85+1.00i,0.09-1.31i,-
-0.34+0.36i)=d.sub.1.sup.p
Seq7=one shift to the right of Seq6
Seq8=so on . . . .
With this time shift and since the complete time domain signal is
the summation of all pilot (and data) signals on different
subcarriers, the average power over different timeslots would be
almost equal to each other and large power variations will not
occur between time samples of the symbol-block. Some steps for
achieving this are described with reference to FIGS. 13-14.
Referring to FIG. 13, a flow chart 1300 shows some steps that may
be used in the method for generating a modulation signal that is
described above with reference to FIG. 8, in accordance with some
embodiments. At step 1305, a second resource element sequence,
M.sub.q.sup.p:.theta.S, of M pilot symbols that form a q.sup.th of
the N subcarriers is determined, wherein q.noteq.n, and wherein
pilot frequency domain samples, r.sub.q.sup.p(i), 0<i<M-1, of
the q.sup.th subcarrier corresponding to the second resource
element sequence M.sub.q.sup.p:.theta.S are each determined as at
least a phase shift, .theta.(i), of the corresponding pilot
frequency domain samples, r.sub.n.sup.p(i), 0<i<M-1, of the
n.sup.th subcarrier, and wherein .theta.(i)=Qi, and wherein Q is a
phase constant. The phrase "at least" is used because other
techniques that are described below could be combined with this one
to alter the values of the pilot symbols of the first resource
element sequence. The second resource element sequence
M.sub.q.sup.p:.theta.S is multiplexed, at step 1310, with the N-1
resource element sequences that correspond to the N-1 subcarriers
that are not the q.sup.th subcarrier, to form the first resource
block. (Note that the first resource element sequence M.sub.n.sup.p
has already been multiplexed in step 815 described above with
reference to FIG. 8). The phrase "at least" is used because other
techniques that are described below could be combined with phase
shifting to obtain the values of the pilot symbols of the second
resource element sequence. It will be appreciated that using one or
more versions of a pilot frequency domain samples sequence (for
example by applying a phase shift) typically reduces the amount of
amplitude variation of the modulated resource block signal.
Referring to FIG. 14, a flow chart 1400 shows some steps that may
be used in the method for generating a modulation signal that is
described above with reference to FIG. 8, in accordance with some
embodiments. At step 1405, a second resource element sequence,
M.sub.q.sup.p:TS of M pilot symbols that form the resource elements
for a q.sup.th one of the N subcarriers of the first resource block
is determined, wherein q.noteq.n, and wherein the pilot symbols,
d.sub.q.sup.p(i), 0<i<M-1, of the q.sup.th subcarrier are
each determined as a cyclical time shift of the pilot symbols,
d.sub.n.sup.p(i), 0<i<M-1, of the n.sup.th subcarrier. At
step 1410, the second resource element sequence M.sub.q.sup.p:TS is
multiplexed with the N-1 resource element sequences that correspond
to the N-1 subcarriers that are not the q.sup.th subcarrier, to
form the first resource block. (Note that the first resource
element sequence M.sub.n.sup.p has already been multiplexed in step
815 described above with reference to FIG. 8). It will be
appreciated that these embodiments are equivalent to the
embodiments described above with reference to FIG. 13, when an
appropriate phase shift constant Q is chosen.
Referring to FIG. 15, a flow chart 1500 shows some steps that may
be used in the method for generating a modulation signal that is
described above with reference to FIG. 8, in accordance with some
embodiments. At step 1505, a second resource element sequence,
M.sub.q.sup.p:CS, of M pilot symbols that correspond to a q.sup.th
of N subcarriers of a second resource block is determined. The
subcarriers and subcarrier filters of the second resource block may
have the same characteristics of the subcarriers and subcarrier
filters used for the first resource block. The pilot subcarrier, q,
of the second resource block may be the same as the pilot
subcarrier, n, used for the first resource block. A pilot frequency
domain samples sequence, r.sub.q.sup.p:CS, corresponding to the
second resource element sequence M.sub.q.sup.p:CS, comprises
R.sub.q.sup.NZ non-zero magnitude pilot frequency domain samples.
R.sub.q.sup.NZ=R.sub.n.sup.NZ. The R.sub.q.sup.NZ non-zero
magnitude pilot frequency domain samples of the pilot frequency
domain samples sequence r.sub.q.sup.p:CS of the second resource
block are determined as cyclical shifts of the respective
R.sub.n.sup.NZ non-zero magnitude pilot frequency domain samples of
the pilot frequency domain samples sequence r.sub.n.sup.p of the
first resource block. Note that q may be any value from 0 to N-1,
including n. At step 1510, the second resource element sequence
M.sub.q.sup.p:CS is multiplexed with the N-1 resource element
sequences that correspond to the N-1 subcarriers that are not the
q.sup.th subcarrier, to form the second resource block. At step
1515, a second modulation signal is generated by modulating each
subcarrier with a corresponding resource element sequence of the
second resource block, which generates N modulated subcarriers of
the second resource block, and filtering each of the N modulated
subcarriers of the second resource block using a corresponding one
of N subcarrier filters. It will be appreciated that this technique
can be extended to more than two resource element sequences of M
pilot symbols.
Referring to FIG. 16, a flow chart 1600 shows some additional steps
of the method for generating a modulation signal described above
with reference to FIG. 15, in accordance with some embodiments. At
step 1605, a first RF carrier is modulated with the first
modulation signal to generate a first modulated RF signal. The
first modulated RF signal is coupled to a first antenna port. At
step 1610, a second RF carrier with the second modulation signal to
generate a second modulated RF signal. The second modulated RF
signal is coupled to a second antenna port, wherein the second
antenna port is different than the first antenna port. The first
and second modulation RF signals may be transmitted simultaneously,
in synchronism. An "antenna port" according to certain embodiments
may be a logical port that may correspond to a beam (resulting from
beam forming) or may correspond to a physical antenna at an
electronic device. An antenna port can be defined such that the
channel over which a symbol on the antenna port is conveyed can be
inferred from the channel over which another symbol on the same
antenna port is conveyed. In some embodiments, a physical antenna
may map directly to a single antenna port, in which case an antenna
port corresponds to an actual physical antenna. Alternately, a set
or subset of physical antennas, or antenna set, may be mapped to
one or more antenna ports after applying complex weights, a cyclic
delay, or both to the signal on each physical antenna. The physical
antenna set may have antennas from a single electronic device or
from multiple electronic devices. The weights may be fixed as in an
antenna virtualization scheme, such as cyclic delay diversity
(CDD). The pilot signals associated with an antenna port may be
specific or common to all destination devices. The procedure used
to derive antenna ports from physical antennas may be specific to
an electronic device implementation and transparent to other
electronic devices. In accordance with some embodiments, the first
antenna port and the second antenna port may be quasi-located such
that the large-scale properties of the channel over which a symbol
on first antenna port is conveyed can be inferred from the channel
over which a symbol on the second antenna port is conveyed. The
large-scale properties can include one or more of delay spread,
Doppler spread, Doppler shift, average gain, and average delay.
Referring to FIG. 17, a flow chart 1700 shows some steps that may
be used in the method for generating a modulation signal described
above with reference to FIG. 8, in accordance with some
embodiments. At step 1705, a second resource element sequence,
M.sub.q.sup.p:U, of M pilot symbols that correspond to a q.sup.th
of N subcarriers of a second resource block is determined. The
pilot subcarrier, q, of the second resource block may be the same
as the pilot subcarrier, n, used for the first resource block. A
pilot frequency domain samples sequence, r.sub.q.sup.p:U,
corresponding to the second resource element sequence
M.sub.q.sup.p:U, comprises R.sub.q.sup.NZ non-zero magnitude
values. R.sub.q.sup.NZ=R.sub.n.sup.NZ. The R.sub.n.sup.NZ non-zero
magnitude pilot frequency domain samples of the pilot frequency
domain samples sequence r.sub.n.sup.p are based on a first
Zadoff-Chu sequence having a first base. The R.sub.q.sup.NZ
non-zero magnitude pilot frequency domain samples of the pilot
frequency domain samples sequence r.sub.q.sup.p:U are based on a
second Zadoff-Chu sequence having a second base, preferably of the
same length as the first ZC sequence. Note that q may be any value
from 0 to N-1, including n, and the first base is different than
the second base. At step 1710, the second resource element sequence
M.sub.q.sup.p:U is multiplexed with the N-1 resource element
sequences that correspond to the N-1 subcarriers that are not the
q.sup.th subcarrier to form the second resource block. At step
1715, a second modulation signal is generated by modulating each
subcarrier with a corresponding resource element sequence of the
second resource block, which generates N modulated subcarriers, and
filtering each of the N modulated subcarriers using a corresponding
one of N subcarrier filters.
Referring to FIG. 18, a flow chart 1800 shows some additional steps
of the method for generating a modulation signal described above
with reference to FIG. 17, in accordance with some embodiments. At
step 1805, a first RF carrier is modulated with the first
modulation signal to generate a first modulated RF signal. The
first modulated RF signal is coupled to a first antenna port. At
step 1810, a second RF carrier with the second modulation signal to
generate a second modulated RF signal. The second modulated RF
signal is coupled to a second antenna port, wherein the second
antenna port is different than the first antenna port.
Zadoff-Chu sequences keep their constant amplitude and correlation
property after FFT and IFFT operations, meaning that if they are
orthogonal in one domain they will be orthogonal in other domain as
well. Another important point is that, due to the way that the ZC
sequences are generated, the effective length of the sequences are
R.sup.NZ not M. Therefore at most R.sup.NZ different cyclic shifts
of the Zadoff-Chu sequence can be used to generate fully orthogonal
Zadoff-Chu pilot signals. Different bases of the same Zadoff-Chu
sequence length may be also be used to achieve a high degree of
quasi-orthogonality (low cross-correlation) in some embodiments. It
is this property that is described with reference to FIGS. 17 and
18. In cases in which different base ZC sequences are used, these
sequences are not completely orthogonal but have a correlation
of
##EQU00005## which may be sufficiently small in long resource
blocks to provide a desired accuracy of signal recovery in a
receiver. Note that for small resource block lengths,
##EQU00006## will not be a small number and application of
Zadoff-Chu sequences with different bases may result in high
interference and inaccurate channel estimation).
Benefits of embodiments described herein with reference to FIGS.
15-18 are that they can support simultaneous transmission of
multiple orthogonal pilots (either in a multiple antenna case or in
a case of inter-cell coordination transmissions from multiple
cellular base stations for reducing the interference over pilot
signals). To multiplex different pilots the property of the
Zadoff-Chu sequences is used that Zadoff-Chu sequences of the same
length and base are orthogonal to each other if they have different
cyclic shift offset values, i.e., Zadoff-Chu sequences of any
length have an "ideal" periodic autocorrelation (i.e., the
correlation with the circularly shifted version of itself is a
delta function).
The techniques described herein above as described with reference
to FIGS. 13-18, may be used in combination. As an example, in a
resource block of length 5 symbol-block (M=5) with .alpha.=0.3,
there may be three interference-free samples. So, for up to 3 pilot
signals a multiplexing of three Zadoff-Chu sequences (different
cyclic shift values) with the same base u can be used:
r.sub.u.sup.(0)(k) (no cyclic shift), r.sub.u.sup.(1)(k) (cyclic
shift value of 1), and r.sub.u.sup.(2)(k) (cyclic shift value of
2), where gcd(u, 3)=1, i.e., u=1 or 2. If more pilot symbol
sequences are needed, ZC sequences can be added with base
u.sub.n.noteq.u.sub.q, wherein the gcd(u.sub.q, 3)=1. Using both
cyclic shifting and ZC sequences of the same length and different
bases is a combination of techniques described with reference to
FIGS. 15-18 that may be used in a signal transmitted on one antenna
port or two or more signals formulated to simultaneously transmit
resource blocks including different data symbols on different
antenna ports. Also, the techniques with reference to FIGS. 13-14
of applying a phase shift to the pilot frequency domain samples or
cyclic time shift to the pilot symbols on different pilot
subcarriers of signal transmitted from a given antenna can be
combined with the techniques with reference to FIGS. 15-18 of
multiple orthogonal pilots signal generation for simultaneous
transmission from different antenna ports to reduce the power
variations of signals across the time slots or between symbols of a
symbol-block from each antenna port of the different antenna
ports.
Referring to FIG. 19, a flow chart 1900 shows some steps of a
method for receiving a carrier demodulated RF signal, in accordance
with some embodiments. At step 1905, a subcarrier that includes
known pilot symbols within a resource block of the carrier
demodulated RF is identified, wherein the known pilot symbols are
formed to be free from inter-subcarrier interference. At step 1910,
synchronization is performed to a clock of the carrier demodulated
RF signal. At step 1915, a channel estimate based on carrier
demodulated RF signal and the known pilot symbols is determined. At
step 1920, inter-subcarrier interference between at least two
subcarriers of data symbols is removed iteratively without
determining a new channel estimate.
The iteration in step 1920 comprises, in some embodiments, a first
estimate of the data symbols on the data subcarriers in the
resource block is determined using the channel estimate assuming no
inter-subcarrier interference between two adjacent subcarriers.
This first estimate of data symbols forms the latest or most recent
estimate of the data symbol estimate for the iterative (one or
iteration) interference canceller. On an iteration of the
interference canceller, for a data subcarrier, inter-subcarrier
interference from at least one adjacent subcarrier of the data
subcarrier is estimated based on the most recent estimate of the
data symbol sequence on the at least one adjacent subcarrier, the
subcarrier filter, and other characteristics of the resource block
modulator. The estimated inter-subcarrier interference is
subtracted from the carrier demodulated RF signal, and the data
symbol sequence on the data subcarrier is re-estimated and becomes
the most recent estimate of the data symbol sequence on the data
subcarrier. This process (estimation of the inter-subcarrier
interference on a data subcarrier, subtracting the estimate, and
re-estimating the data symbol sequence on the data subcarrier
resulting in the most recent estimate the data symbol sequence on
the data subcarrier) is repeated for each data subcarrier
(preferably sequentially in data subcarrier index) in the resource
block using the latest or most recent estimate of the data symbol
sequences on the adjacent subcarriers to estimate the
inter-subcarrier interference on the data subcarrier. Once the data
symbols on all the data subcarriers of the resource block are
re-estimated, a next iteration of the interference canceller can be
performed. The number of iterations may continue until a
convergence criteria is met (e.g., packet is successfully decoded)
or a maximum iteration limit is reached. In some embodiments,
interference cancellation begins with the data subcarrier adjacent
to the pilot subcarrier and sequentially proceeds to the other data
subcarriers away from the pilot subcarrier.
It will be appreciated that an electronic device such as some of
those described with reference to FIG. 1 can perform the methods
described with reference to FIGS. 8-18.
It will be appreciated that an electronic device such as those
described with reference to FIG. 2 can perform the methods
described with reference to FIG. 19.
It should be apparent to those of ordinary skill in the art that
for the methods described herein other steps may be added or
existing steps may be removed, modified or rearranged without
departing from the scope of the methods. Also, the methods are
described with respect to the apparatuses described herein by way
of example and not limitation, and the methods may be used in other
systems.
In this document, relational terms such as first and second, top
and bottom, and the like may be used solely to distinguish one
entity or action from another entity or action without necessarily
requiring or implying any actual such relationship or order between
such entities or actions. The terms "comprises," "comprising," or
any other variation thereof, are intended to cover a non-exclusive
inclusion, such that a process, method, article, or apparatus that
comprises a list of elements does not include only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus. An element preceded by
"comprises . . . a" does not, without more constraints, preclude
the existence of additional identical elements in the process,
method, article, or apparatus that comprises the element. The term
"coupled" as used herein is defined as connected, although not
necessarily directly and not necessarily mechanically.
Reference throughout this document are made to "one embodiment",
"certain embodiments", "an embodiment" or similar terms The
appearances of such phrases or in various places throughout this
specification are not necessarily all referring to the same
embodiment. Furthermore, the particular features, structures, or
characteristics attributed to any of the embodiments referred to
herein may be combined in any suitable manner in one or more
embodiments without limitation.
The term "or" as used herein is to be interpreted as an inclusive
or meaning any one or any combination. Therefore, "A, B or C" means
"any of the following: A; B; C; A and B; A and C; B and C; A, B and
C". An exception to this definition will occur only when a
combination of elements, functions, steps or acts are in some way
inherently mutually exclusive.
The processes illustrated in this document, for example (but not
limited to) the method steps described in FIGS. 8-19, may be
performed using programmed instructions contained on a computer
readable medium which may be read by processor of a CPU. A computer
readable medium may be any tangible medium capable of storing
instructions to be performed by a microprocessor. The medium may be
one of or include one or more of a CD disc, DVD disc, magnetic or
optical disc, tape, and silicon based removable or non-removable
memory. The programming instructions may also be carried in the
form of packetized or non-packetized wireline or wireless
transmission signals.
It will be appreciated that some embodiments may comprise one or
more generic or specialized processors (or "processing devices")
such as microprocessors, digital signal processors, customized
processors and field programmable gate arrays (FPGAs) and unique
stored program instructions (including both software and firmware)
that control the one or more processors to implement, in
conjunction with certain non-processor circuits, some, most, or all
of the functions of the methods and/or apparatuses described
herein. Alternatively, some, most, or all of these functions could
be implemented by a state machine that has no stored program
instructions, or in one or more application specific integrated
circuits (ASICs), in which each function or some combinations of
certain of the functions are implemented as custom logic. Of
course, a combination of the approaches could be used.
Further, it is expected that one of ordinary skill, notwithstanding
possibly significant effort and many design choices motivated by,
for example, available time, current technology, and economic
considerations, when guided by the concepts and principles
disclosed herein will be readily capable of generating such stored
program instructions and ICs with minimal experimentation.
In the foregoing specification, specific embodiments have been
described. However, one of ordinary skill in the art appreciates
that various modifications and changes can be made without
departing from the scope of the present invention as set forth in
the claims below. Accordingly, the specification and figures are to
be regarded in an illustrative rather than a restrictive sense, and
all such modifications are intended to be included within the scope
of present invention. The benefits, advantages, solutions to
problems, and any element(s) that may cause any benefit, advantage,
or solution to occur or become more pronounced are not to be
construed as a critical, required, or essential features or
elements of any or all the claims. The invention is defined solely
by the appended claims including any amendments made during the
pendency of this application and all equivalents of those claims as
issued.
* * * * *